Kvalita vody je důležitá.

Because Czech uses the genitive case after a noun like kvalita when you mean the quality of something.

• kvalita = quality
• voda = water
• vody = of water

So:

• Kvalita vody = the quality of water

This is very common in Czech:

• barva auta = the color of the car
• cena domu = the price of the house
• chuť jídla = the taste of the food

So vody is not plural here. It is singular genitive.

Kvalita is in the nominative singular because it is the subject of the sentence.

In Kvalita vody je důležitá, the thing being talked about is the quality of water, so kvalita is the grammatical subject.

A rough structure is:

• Kvalita vody = subject
• je = is
• důležitá = important

Because adjectives in Czech must agree with the noun they describe.

The noun kvalita is:

• feminine
• singular
• nominative

So the adjective must also be:

• feminine
• singular
• nominative

That gives důležitá.

Compare:

• důležitý = masculine singular
• důležitá = feminine singular
• důležité = neuter singular or plural in some contexts

Since kvalita is feminine, důležitá is the correct form.

Here, je is the 3rd person singular of být (to be), meaning is.

In this sentence, standard Czech normally uses it:

• Kvalita vody je důležitá. = The quality of water is important.

Czech sometimes drops forms of to be in informal speech, headlines, notes, or very colloquial style, but for a normal full sentence like this, je is expected.

So for learners, the safest rule is:

• use je in sentences like this

Czech has no articles like the or a/an.

So Kvalita vody can correspond to English expressions like:

• the quality of water
• water quality

Which English version sounds best depends on context.

Czech often leaves definiteness unstated, and you understand it from the situation.

Yes. Czech word order is more flexible than English, because case endings show grammatical relationships.

The neutral, straightforward order is:

• Kvalita vody je důležitá.

But other orders are possible for emphasis, for example:

• Důležitá je kvalita vody.
  = What is important is the quality of water.

This sounds more emphatic or contrastive.

Even though the order can change, the most natural basic version for learners is the original one.

No. In this sentence, vody is singular genitive of voda.

This can confuse learners because some Czech forms look like plural forms. But here the meaning is clearly:

• of water, not waters

So:

• voda = water
• vody = of water

A helpful rough pronunciation is:

• doo-LEH-zhi-taa

A few important points:

• ů sounds like a long oo
• ž sounds like the s in measure
• stress in Czech is usually on the first syllable, so: DŮležitá

So the stress is on dů, not on the middle of the word.

The accent marks in Czech usually show vowel length or a special sound.

In důležitá:

• ů = a long u
• á = a long a

These are part of the correct spelling and pronunciation.

In kvalita, the vowels are short, so there are no accent marks.

Vowel length matters in Czech, so it is worth paying attention to it.

Yes. It is a normal and natural Czech way to express that idea.

Czech often uses:

• a noun + another noun in the genitive

So instead of forming something like an English noun-noun compound (water quality), Czech commonly says:

• kvalita vody = quality of water

This pattern is extremely common and useful to learn.

Yes, but it means something different.

• Voda je důležitá. = Water is important.
• Kvalita vody je důležitá. = The quality of water is important.

The original sentence focuses specifically on quality, not just on water itself.

So both are correct, but they express different ideas.

It describes kvalita, not vody.

You can tell because důležitá is in the feminine singular nominative, matching kvalita.

If it were describing voda, the sentence structure would be different, for example:

• Voda je důležitá.

In the original sentence, vody is inside the phrase kvalita vody and depends on kvalita in the genitive.

The dictionary forms are:

• kvalita = quality
• voda = water
• být = to be
• důležitý = important

In the sentence, these appear as:

• kvalita → unchanged
• voda → vody because of the genitive
• být → je
• důležitý → důležitá to agree with kvalita